This invention relates to a method of controlling the quantity of fuel being supplied to an internal combustion engine after the start of the engine, and more particularly to such a control method, which is adapted to set the quantity of fuel being supplied to the engine immediately after cranking thereof to appropriate values in response to the temperature of fuel injection valves.
In order to prevent engine stall after the start of the engine and obtain smooth acceleration after the engine start, a fuel supply control method has been proposed by the assignee of the present application in Japanese Provisional Patent Publication (Kokai) No. 59-46329, which comprises setting an initial value of a fuel increment which is applied immediately after the cranking of the engine, to a value corresponding to a product of a value of an engine coolant temperaturedependent fuel increasing coefficient KTW, which decreases as the engine coolant temperature representative of the engine temperature increases, and a value of an after-start fuel increasing coefficient KAST, subsequently decreasing the initial value of the fuel increment by a predetermined value upon generation of each pulse of a top-dead-center (TDC) signal, and supplying the engine with a quantity of fuel set by the use of the thus set fuel increment.
However, this conventional method, according to which the initial value of the fuel increment is set in response to the engine temperature, has a problem that, when the engine temperature at the start of the engine is so high that the fuel is boiling, it is impossible to effect optimal fuel supply during a period following the start of the engine. For example, if the engine is once stopped and started soon again, it often happens that the temperature inside the fuel injection valves is higher than the boiling point of the fuel so that bubbles are apt to be formed in the fuel within the fuel injection valves. As a result, the fuel injected into the intake pipe of the engine contains these bubbles so that the air-fuel mixture supplied to the engine is in effect leaned, whereby engine stall is apt to occur and it becomes difficult to obtain smooth acceleration of the engine after the start thereof.